Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
  • C03C3/00—Glass compositions
  • C03C3/04—Glass compositions containing silica
  • C03C3/076—Glass compositions containing silica with 40% to 90% silica, by weight
  • C03C3/089—Glass compositions containing silica with 40% to 90% silica, by weight containing boron
  • C03C3/091—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium
  • C03C3/093—Glass compositions containing silica with 40% to 90% silica, by weight containing boron containing aluminium containing zinc or zirconium
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S501/00—Compositions: ceramic
  • Y10S501/90—Optical glass, e.g. silent on refractive index and/or ABBE number
  • Y10S501/903—Optical glass, e.g. silent on refractive index and/or ABBE number having refractive index less than 1.8 and ABBE number less than 70

Definitions

• circuit patterns are printed on a substrate wafer (Si, or GaAs) by the following generalized process.
• a silicon wafer is oxidized to form a thin SiO 2 surface layer.
• the oxidized surface is then covered by a photoresist material which polymerizes on exposure to UV radiation or electron beams.
• the wafer is aligned with a photomask bearing a negative of the circuit pattern to be printed and exposed to UV light or an electron beam. Areas where the radiation passes through the photomask are polymerized, and areas where radiation is blocked by the photomask are not polymerized. Unpolymerized photoresist is stripped away.
• the exposed SiO 2 surface is then removed, exposing the underlying silicon which can then be doped with various impurities to fabricate the semiconductor device itself. Finally, the overlying polymerized photoresist is itself stripped away.
• the function of the photomask is to define the circuit pattern on the substrate. Production of complex, integrated circuits involves as many as 12 or more sequences of the above photolighographic process.
• the first type may be termed "high-expansion” and generally utilizes soda-lime (window glass) and white crown glass types having coefficients of thermal expansion ⁇ 100 ⁇ 10 -7 °C. -1 .
• Circuit designs are printed on the mask using film emulsions or by a combination iron-chromium coating. Because of the high expansion coefficient, the photomasks are used in contact with the substrate to minimize distortion effects. This contact leads to erosion of the circuit pattern, and the photomasks can only be used for a limited number of exposures, making their use undesirably expensive.
• the second category is that of low-expansion photomasks. These are usually borosilicate and aluminosilicate glasses having coefficients of thermal expansion ⁇ 50 ⁇ 10 -7 ° C. -1 . These lower thermal expansion materials permit noncontact exposure of wafers and thus longer mask lifetime and more critical circuit resoution (2-5 ⁇ m). Again, alkali content of these glasss is a critical problem because of its influence in the formation of pinhole defects in the photomask. The connection between alkali content and pinhole defects in photomasks has been discussed by Izumitani et al, "Surface Texture Problems of High Precision Glass Substrates for Photomasks", Hoya Optics, Menlo Park, CA.
• the third category of photomasks comprises ultra-low-expansion materials, typically fused silica, with coefficients of thermal expansion below 1 ⁇ 10 -7 °C. -1 .
• the very low expansion coefficient is useful as it induces minimal distortion in the applied circuit pattern and thus allows higher resolution.
• fused silica is alkali-free, no alkali-related pitting or other defects occur during photomask fabrication.
• fused silica cannot be made in conventional melting units used for multicomponent glasses, is more expensive to produce, and is often of inferior optical quality to what is possible in the low-expansion class of materials.
• integrated circuit production primarily utilizes the first two classes of materials; high-expansion photomasks for low density circuity, and low-expansion materials for more critical applications.
• Tables 1 and 2 give a summary of composition and properties of the most widely used low-expansion photomask glasses (LE-30, E-6, CGW7740, and PMG-1).
• It is still another object of the present invention provide an alkali-free, low-expansion glass suitable for use as a photomask material and also having other physical and optical properties equivalent to or better than existing low-expansion materials, thereby avoiding alkali-associated defects in the manufacture and use of the photomask.
• an optical quality glass which has a refractive index n d of at least 1.50, perferably 1.54-1.57, an Abbe number Vd of at least 55, preferably 56-59, a density of not more than 3.0, preferably 2.80-2.91, and a coefficient of thermal expanion (20°-300° C.) (CTE) of not more than 40.5 ⁇ 10 -7 °C. -1 , preferably 35.5-39.0 ⁇ 10 -7 °C. -1 , which does not contain alkali and which contains at least 90 mol. % of SiO 2 , B 2 O 3 , Al 2 O 3 , MgO, CaO, BaO and ZnO and consists essentially of in weight percent:
• composition of this invention consists essentially of:
• Sum MgO+CaO+BaO+ZnO 13-31.5, preferably 15-31.5, most preferably 23-26.5, typically about 26 molar percent.
• the low expansion glass composition of this invention is unlike any other prior art glass.
• the limits in terms of weight percent or the essentially equivalent mole percentages) are critical for each of the ingredients of the glass, especially of those for barium oxide and zinc oxide.
• Magnesium oxide is not a necessary component in the glass composition of this invention; however, it is preferred that this component be present. Amounts of magnesium oxide higher than the specified range will be immiscible in the composition, will cause the glass to become unstable and crystallization will be observed. The same is true for the optional calcium oxide ingredient with respect to its specified range.
• Barium oxide is one of the most critical ingredients in the glass composition of this invention, e.g., the coefficient of thermal expansion will change to a larger extent upon variations in its content than for the other components of the glass. Amounts of barium oxide less than the specified range will cause phase separation in the glass; amounts higher than specified will cause the CTE to be too high. It is generally preferred that the amount of barium oxide be about 9.15-9.35 weight percent (about 4.24-4.26 mole percent).
• the zinc oxide content very critical to the achievement of the desired properties for the glass composition of this invention is the zinc oxide content. Amounts lower than specified will cause the CTE to be too high; amounts higher than specified will be immiscible in the glass composition and will cause the glass to become unstable. In addition, crystallization will be observed. Particularly preferred amounts of zinc oxide are about 14.5-17.1 weight percent (about 12.5-15 mole percent).
• cerium oxide, lead oxide and the refining agents antimony oxide and arsenic oxide are also optional ingredients. Amounts of cerium oxide higher than specified will cause the transmission properties to be too low in the important range of 350-700 nm. Amounts of the refining agents which are too high will cause the glass to refine improperly. Amounts of lead oxide higher than specified will cause the CTE to be too high.
• each range defined above includes many narrower ranges within it which are part of this invention. For example, a range of 12-18 wt. % is given for ZnO. This range includes the narrower ranges 12.1-18%, 12.0-17.9%, 12.1-17.9%, 12.2-18%, etc., i.e., the narrower included ranges wherein one or both of the endpoints are varied one or more multiples of 0.1%.
• the general range 12-18% also includes the narrower ranges 12.5-18%, 12.0-17.5%, 12.5-17.5%, etc, as well as the mentioned preferred ranges such as 14.5-17.1% for ZnO or even narrower ranges such as 14.6-15.1%.
• the latter is about the smallest practical differential that can be maintained with normal manufacturing procedures.
• the ranges of other ingredients similarly define corresponding narrower ranges.
• the glass of this invention can be prepared using fully conventional techniques normally employed for glasses of this type.
• the usual raw materials corresponding to the oxides required in the glasses of this invention e.g., oxides per se, carbonates, nitrates, hydroxides, etc.
• Typical melting temperatures are 1200°-1600° C.
• Conventional crucibles or tanks, e.g., graphite coated, ceramic or platinum containers can be used.
• the homogeneous melt is then further treated conventionally, e.g., refined, casted into molds, gradually cooled, etc.
• a particularly preferred use for the low-expansion glass of this invention is in photomasking applications as described above.
• the glass of this invention will be useful in a wide variety of other uses, for example, without intending to limit the scope of the uses of the glass of this invention, to applications including substrates for photovoltaic devices, windows, lenses, mirrors, etc., or other optical components requiring its unique properties, e.g., those having high thermal shock resistance, for general purposes where high quality mirrors with minimized thermal distortion effects are needed, etc.
• the glass of this invention can be cast, molded or otherwise formed into any desired shape or configuration for any of the many uses to which it is applicable.
• the mixed batch is then melted in a 0.5 liter capacity platinum crucible heated by induction at 1530° C. Following melting, the glass is homogenized and refined at 1580° C. for 5 hours. The glass is then cast into graphite-coated steel molds and annealed using an annealing temperature of about 700° C. and a cooling rate of 30° C./hr. The strain-free, annealed glass can then be ground and polished to prepare optical components using conventional techniques.
• Table 3 summarizes several examples of glasses of this invention as well as their properties. Examples A, B and C are preferred.

Landscapes

• Chemical & Material Sciences (AREA)
• Life Sciences & Earth Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• General Chemical & Material Sciences (AREA)
• Geochemistry & Mineralogy (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Glass Compositions (AREA)
• Formation Of Insulating Films (AREA)
• Preparing Plates And Mask In Photomechanical Process (AREA)

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Cited By (24)

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Citations (10)

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• 1984
  • 1984-05-08 US US06/608,304 patent/US4554259A/en not_active Expired - Lifetime
• 1985
  • 1985-05-04 DE DE3516020A patent/DE3516020C2/de not_active Expired - Fee Related
  • 1985-05-07 FR FR8506911A patent/FR2564087B1/fr not_active Expired
  • 1985-05-07 GB GB08511542A patent/GB2158431B/en not_active Expired
  • 1985-05-08 JP JP60096170A patent/JPS60239342A/ja active Granted

Patent Citations (10)

Non-Patent Citations (2)

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